Prediction mode signaling in video coding

ABSTRACT

A method of decoding video data, comprising: receiving, from bitstream, video data corresponding to a non-skip mode coded block; determining a parameter set associated with the non-skip mode coded block; if the parameter set satisfies a first condition, retrieving a first syntax element from the bitstream; if the parameter set satisfies a second condition, retrieving a second syntax element from the bitstream; if the parameter set satisfies a third condition, retrieving a third syntax element from the bitstream; decoding the video data corresponding to the non-skip mode coded block using palette mode when the first syntax element and the third syntax element have the first value; decoding the video data using intra prediction mode when the first syntax element has the first value and the third syntax element has a second value; and decoding the video data using inter prediction mode when the first syntax element has the second value.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of PCT Application No.PCT/US2020/049653, entitled “PREDICTION MODE SIGNALING IN VIDEO CODING”filed on Sep. 8, 2020, which claims priority to U.S. ProvisionalApplication No. 62/897,292, entitled “PREDICTION MODE SIGNALING IN VIDEOCODING” filed on Sep. 7, 2019, both of which are incorporated byreference in their entirety.

TECHNICAL FIELD

The present application generally relates to video data encoding anddecoding, and in particular, to method and system for prediction modessignaling in video coding.

BACKGROUND

Digital video is supported by a variety of electronic devices, such asdigital televisions, laptop or desktop computers, tablet computers,digital cameras, digital recording devices, digital media players, videogaming consoles, smart phones, video teleconferencing devices, videostreaming devices, etc. The electronic devices transmit, receive,encode, decode, and/or store digital video data by implementing videocompression/decompression standards as defined by MPEG-4, ITU-T H.263,ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), HighEfficiency Video Coding (HEVC), and Versatile Video Coding (VVC)standard. Video compression typically includes performing spatial (intraframe) prediction and/or temporal (inter frame) prediction to reduce orremove redundancy inherent in the video data. For block-based videocoding, a video frame is partitioned into one or more slices, each slicehaving multiple video blocks, which may also be referred to as codingtree units (CTUs). Each CTU may contain one coding unit (CU) orrecursively split into smaller CUs until the predefined minimum CU sizeis reached. Each CU (also named leaf CU) contains one or multipletransform units (TUs) and each CU also contains one or multipleprediction units (PUs). Each CU can be coded in either intra, inter orIBC modes. Video blocks in an intra coded (I) slice of a video frame areencoded using spatial prediction with respect to reference samples inneighbor blocks within the same video frame. Video blocks in an intercoded (P or B) slice of a video frame may use spatial prediction withrespect to reference samples in neighbor blocks within the same videoframe or temporal prediction with respect to reference samples in otherprevious and/or future reference video frames.

Spatial or temporal prediction based on a reference block that has beenpreviously encoded, e.g., a neighbor block, results in a predictiveblock for a current video block to be coded. The process of finding thereference block may be accomplished by block matching algorithm.Residual data representing pixel differences between the current blockto be coded and the predictive block is referred to as a residual blockor prediction errors. An inter-coded block is encoded according to amotion vector that points to a reference block in a reference frameforming the predictive block, and the residual block. The process ofdetermining the motion vector is typically referred to as motionestimation. An intra coded block is encoded according to an intraprediction mode and the residual block. For further compression, theresidual block is transformed from the pixel domain to a transformdomain, e.g., frequency domain, resulting in residual transformcoefficients, which may then be quantized. The quantized transformcoefficients, initially arranged in a two-dimensional array, may bescanned to produce a one-dimensional vector of transform coefficients,and then entropy encoded into a video bitstream to achieve even morecompression.

The encoded video bitstream is then saved in a computer-readable storagemedium (e.g., flash memory) to be accessed by another electronic devicewith digital video capability or directly transmitted to the electronicdevice wired or wirelessly. The electronic device then performs videodecompression (which is an opposite process to the video compressiondescribed above) by, e.g., parsing the encoded video bitstream to obtainsyntax elements from the bitstream and reconstructing the digital videodata to its original format from the encoded video bitstream based atleast in part on the syntax elements obtained from the bitstream, andrenders the reconstructed digital video data on a display of theelectronic device.

With digital video quality going from high definition, to 4K×2K or even8K×4K, the amount of vide data to be encoded/decoded growsexponentially. It is a constant challenge in terms of how the video datacan be encoded/decoded more efficiently while maintaining the imagequality of the decoded video data.

SUMMARY

The present application describes implementations related to video dataencoding and decoding and, more particularly, to system and method forprediction modes signaling in video coding.

According to a first aspect of the present application, a method ofdecoding video data is performed at a computing device having one ormore processors and memory storing a plurality of programs to beexecuted by the one or more processors. The method comprises: receiving,from bitstream, video data corresponding to a non-skip mode coded block;determining a parameter set associated with the non-skip mode codedblock; if the parameter set satisfies a first condition, retrieving afirst syntax element from the bitstream; if the parameter set satisfiesa second condition, retrieving a second syntax element from thebitstream; if the parameter set satisfies a third condition, retrievinga third syntax element from the bitstream; decoding the video datacorresponding to the non-skip mode coded block using palette mode whenthe first syntax element and the third syntax element have the firstvalue; decoding the video data using intra prediction mode when thefirst syntax element has the first value and the third syntax elementhas a second value; and decoding the video data using inter predictionmode when the first syntax element has the second value.

According to a second aspect of the present application, a computingdevice includes one or more processors, memory and a plurality ofprograms stored in the memory. The programs, when executed by the one ormore processors, cause the computing device to perform operations asdescribed above.

According to a third aspect of the present application, a non-transitorycomputer readable storage medium stores a plurality of programs forexecution by a computing device having one or more processors. Theprograms, when executed by the one or more processors, cause thecomputing device to perform operations as described above.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the implementations and are incorporated herein andconstitute a part of the specification, illustrate the describedimplementations and together with the description serve to explain theunderlying principles. Like reference numerals refer to correspondingparts.

FIG. 1 is a block diagram illustrating an exemplary video encoding anddecoding system in accordance with some implementations of the presentdisclosure.

FIG. 2 is a block diagram illustrating an exemplary video encoder inaccordance with some implementations of the present disclosure.

FIG. 3 is a block diagram illustrating an exemplary video decoder inaccordance with some implementations of the present disclosure.

FIGS. 4A-4E are block diagrams illustrating how a frame is recursivelyquad-tree partitioned into multiple video blocks of different sizes inaccordance with some implementations of the present disclosure.

FIG. 5 is a block diagram illustrating different prediction modes of acoding unit in accordance with some implementations of the presentdisclosure.

FIG. 6 is a flowchart illustrating an exemplary process by which a videocoder implements the techniques of signaling prediction mode inaccordance with some implementations of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to specific implementations,examples of which are illustrated in the accompanying drawings. In thefollowing detailed description, numerous non-limiting specific detailsare set forth in order to assist in understanding the subject matterpresented herein. But it will be apparent to one of ordinary skill inthe art that various alternatives may be used without departing from thescope of claims and the subject matter may be practiced without thesespecific details. For example, it will be apparent to one of ordinaryskill in the art that the subject matter presented herein can beimplemented on many types of electronic devices with digital videocapabilities.

FIG. 1 is a block diagram illustrating an exemplary system 10 forencoding and decoding video blocks in parallel in accordance with someimplementations of the present disclosure. As shown in FIG. 1, system 10includes a source device 12 that generates and encodes video data to bedecoded at a later time by a destination device 14. Source device 12 anddestination device 14 may comprise any of a wide variety of electronicdevices, including desktop or laptop computers, tablet computers, smartphones, set-top boxes, digital televisions, cameras, display devices,digital media players, video gaming consoles, video streaming device, orthe like. In some implementations, source device 12 and destinationdevice 14 are equipped with wireless communication capabilities.

In some implementations, destination device 14 may receive the encodedvideo data to be decoded via a link 16. Link 16 may comprise any type ofcommunication medium or device capable of moving the encoded video datafrom source device 12 to destination device 14. In one example, link 16may comprise a communication medium to enable source device 12 totransmit the encoded video data directly to destination device 14 inreal-time. The encoded video data may be modulated according to acommunication standard, such as a wireless communication protocol, andtransmitted to destination device 14. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 12 to destination device 14.

In some other implementations, the encoded video data may be transmittedfrom output interface 22 to a storage device 32. Subsequently, theencoded video data in storage device 32 may be accessed by destinationdevice 14 via input interface 28. Storage device 32 may include any of avariety of distributed or locally accessed data storage media such as ahard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, storage device 32 maycorrespond to a file server or another intermediate storage device thatmay hold the encoded video data generated by source device 12.Destination device 14 may access the stored video data from storagedevice 32 via streaming or downloading. The file server may be any typeof computer capable of storing encoded video data and transmitting theencoded video data to destination device 14. Exemplary file serversinclude a web server (e.g., for a website), an FTP server, networkattached storage (NAS) devices, or a local disk drive. Destinationdevice 14 may access the encoded video data through any standard dataconnection, including a wireless channel (e.g., a Wi-Fi connection), awired connection (e.g., DSL, cable modem, etc.), or a combination ofboth that is suitable for accessing encoded video data stored on a fileserver. The transmission of encoded video data from storage device 32may be a streaming transmission, a download transmission, or acombination of both.

As shown in FIG. 1, source device 12 includes a video source 18, a videoencoder 20 and an output interface 22. Video source 18 may include asource such as a video capture device, e.g., a video camera, a videoarchive containing previously captured video, a video feed interface toreceive video from a video content provider, and/or a computer graphicssystem for generating computer graphics data as the source video, or acombination of such sources. As one example, if video source 18 is avideo camera of a security surveillance system, source device 12 anddestination device 14 may form camera phones or video phones. However,the implementations described in the present application may beapplicable to video coding in general, and may be applied to wirelessand/or wired applications.

The captured, pre-captured, or computer-generated video may be encodedby video encoder 20. The encoded video data may be transmitted directlyto destination device 14 via output interface 22 of source device 12.The encoded video data may also (or alternatively) be stored ontostorage device 32 for later access by destination device 14 or otherdevices, for decoding and/or playback. Output interface 22 may furtherinclude a modem and/or a transmitter.

Destination device 14 includes an input interface 28, a video decoder30, and a display device 34. Input interface 28 may include a receiverand/or a modem and receive the encoded video data over link 16. Theencoded video data communicated over link 16, or provided on storagedevice 32, may include a variety of syntax elements generated by videoencoder 20 for use by video decoder 30 in decoding the video data. Suchsyntax elements may be included within the encoded video datatransmitted on a communication medium, stored on a storage medium, orstored a file server.

In some implementations, destination device 14 may include a displaydevice 34, which can be an integrated display device and an externaldisplay device that is configured to communicate with destination device14. Display device 34 displays the decoded video data to a user, and maycomprise any of a variety of display devices such as a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device.

Video encoder 20 and video decoder 30 may operate according toproprietary or industry standards, such as VVC, HEVC, MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. It shouldbe understood that the present application is not limited to a specificvideo coding/decoding standard and may be applicable to other videocoding/decoding standards. It is generally contemplated that videoencoder 20 of source device 12 may be configured to encode video dataaccording to any of these current or future standards. Similarly, it isalso generally contemplated that video decoder 30 of destination device14 may be configured to decode video data according to any of thesecurrent or future standards.

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When implemented partially in software, an electronic devicemay store instructions for the software in a suitable, non-transitorycomputer-readable medium and execute the instructions in hardware usingone or more processors to perform the video coding/decoding operationsdisclosed in the present disclosure. Each of video encoder 20 and videodecoder 30 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device.

FIG. 2 is a block diagram illustrating an exemplary video encoder 20 inaccordance with some implementations described in the presentapplication. Video encoder 20 may perform intra and inter predictivecoding of video blocks within video frames. Intra predictive codingrelies on spatial prediction to reduce or remove spatial redundancy invideo data within a given video frame or picture. Inter predictivecoding relies on temporal prediction to reduce or remove temporalredundancy in video data within adjacent video frames or pictures of avideo sequence.

As shown in FIG. 2, video encoder 20 includes video data memory 40,prediction processing unit 41, decoded picture buffer (DPB) 64, summer50, transform processing unit 52, quantization unit 54, and entropyencoding unit 56. Prediction processing unit 41 further includes motionestimation unit 42, motion compensation unit 44, partition unit 45,intra prediction processing unit 46, and intra block copy (BC) unit 48.In some implementations, video encoder 20 also includes inversequantization unit 58, inverse transform processing unit 60, and summer62 for video block reconstruction. A deblocking filter (not shown) maybe positioned between summer 62 and DPB 64 to filter block boundaries toremove blockiness artifacts from reconstructed video. An in loop filter(not shown) may also be used in addition to the deblocking filter tofilter the output of summer 62. Video encoder 20 may take the form of afixed or programmable hardware unit or may be divided among one or moreof the illustrated fixed or programmable hardware units.

Video data memory 40 may store video data to be encoded by thecomponents of video encoder 20. The video data in video data memory 40may be obtained, for example, from video source 18. DPB 64 is a bufferthat stores reference video data for use in encoding video data by videoencoder 20 (e.g., in intra or inter predictive coding modes). Video datamemory 40 and DPB 64 may be formed by any of a variety of memorydevices. In various examples, video data memory 40 may be on-chip withother components of video encoder 20, or off-chip relative to thosecomponents.

As shown in FIG. 2, after receiving video data, partition unit 45 withinprediction processing unit 41 partitions the video data into videoblocks. This partitioning may also include partitioning a video frameinto slices, tiles, or other larger coding units (CUs) according to apredefined splitting structures such as quad-tree structure associatedwith the video data. The video frame may be divided into multiple videoblocks (or sets of video blocks referred to as tiles). Predictionprocessing unit 41 may select one of a plurality of possible predictivecoding modes, such as one of a plurality of intra predictive codingmodes or one of a plurality of inter predictive coding modes, for thecurrent video block based on error results (e.g., coding rate and thelevel of distortion). Prediction processing unit 41 may provide theresulting intra or inter prediction coded block to summer 50 to generatea residual block and to summer 62 to reconstruct the encoded block foruse as part of a reference frame subsequently. Prediction processingunit 41 also provides syntax elements, such as motion vectors,intra-mode indicators, partition information, and other such syntaxinformation, to entropy encoding unit 56.

In order to select an appropriate intra predictive coding mode for thecurrent video block, intra prediction processing unit 46 withinprediction processing unit 41 may perform intra predictive coding of thecurrent video block relative to one or more neighboring blocks in thesame frame as the current block to be coded to provide spatialprediction. Motion estimation unit 42 and motion compensation unit 44within prediction processing unit 41 perform inter predictive coding ofthe current video block relative to one or more predictive blocks in oneor more reference frames to provide temporal prediction. Video encoder20 may perform multiple coding passes, e.g., to select an appropriatecoding mode for each block of video data.

In some implementations, motion estimation unit 42 determines the interprediction mode for a current video frame by generating a motion vector,which indicates the displacement of a prediction unit (PU) of a videoblock within the current video frame relative to a predictive blockwithin a reference video frame, according to a predetermined patternwithin a sequence of video frames. Motion estimation, performed bymotion estimation unit 42, is the process of generating motion vectors,which estimate motion for video blocks. A motion vector, for example,may indicate the displacement of a PU of a video block within a currentvideo frame or picture relative to a predictive block within a referenceframe (or other coded unit) relative to the current block being codedwithin the current frame (or other coded unit). The predeterminedpattern may designate video frames in the sequence as P frames or Bframes. Intra BC unit 48 may determine vectors, e.g., block vectors, forintra BC coding in a manner similar to the determination of motionvectors by motion estimation unit 42 for inter prediction, or mayutilize motion estimation unit 42 to determine the block vector.

A predictive block is a block of a reference frame that is deemed asclosely matching the PU of the video block to be coded in terms of pixeldifference, which may be determined by sum of absolute difference (SAD),sum of square difference (SSD), or other difference metrics. In someimplementations, video encoder 20 may calculate values for sub-integerpixel positions of reference frames stored in DPB 64. For example, videoencoder 20 may interpolate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference frame. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter prediction coded frame by comparing the position ofthe PU to the position of a predictive block of a reference frameselected from a first reference frame list (List 0) or a secondreference frame list (List 1), each of which identifies one or morereference frames stored in DPB 64. Motion estimation unit 42 sends thecalculated motion vector to motion compensation unit 44 and then toentropy encoding unit 56.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42. Upon receiving themotion vector for the PU of the current video block, motion compensationunit 44 may locate a predictive block to which the motion vector pointsin one of the reference frame lists, retrieve the predictive block fromDPB 64, and forward the predictive block to summer 50. Summer 50 thenforms a residual video block of pixel difference values by subtractingpixel values of the predictive block provided by motion compensationunit 44 from the pixel values of the current video block being coded.The pixel difference values forming the residual vide block may includeluma or chroma difference components or both. Motion compensation unit44 may also generate syntax elements associated with the video blocks ofa video frame for use by video decoder 30 in decoding the video blocksof the video frame. The syntax elements may include, for example, syntaxelements defining the motion vector used to identify the predictiveblock, any flags indicating the prediction mode, or any other syntaxinformation described herein. Note that motion estimation unit 42 andmotion compensation unit 44 may be highly integrated, but areillustrated separately for conceptual purposes.

In some implementations, intra BC unit 48 may generate vectors and fetchpredictive blocks in a manner similar to that described above inconnection with motion estimation unit 42 and motion compensation unit44, but with the predictive blocks being in the same frame as thecurrent block being coded and with the vectors being referred to asblock vectors as opposed to motion vectors. In particular, intra BC unit48 may determine an intra-prediction mode to use to encode a currentblock. In some examples, intra BC unit 48 may encode a current blockusing various intra-prediction modes, e.g., during separate encodingpasses, and test their performance through rate-distortion analysis.Next, intra BC unit 48 may select, among the various testedintra-prediction modes, an appropriate intra-prediction mode to use andgenerate an intra-mode indicator accordingly. For example, intra BC unit48 may calculate rate-distortion values using a rate-distortion analysisfor the various tested intra-prediction modes, and select theintra-prediction mode having the best rate-distortion characteristicsamong the tested modes as the appropriate intra-prediction mode to use.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bitrate(i.e., a number of bits) used to produce the encoded block. Intra BCunit 48 may calculate ratios from the distortions and rates for thevarious encoded blocks to determine which intra-prediction mode exhibitsthe best rate-distortion value for the block.

In other examples, intra BC unit 48 may use motion estimation unit 42and motion compensation unit 44, in whole or in part, to perform suchfunctions for Intra BC prediction according to the implementationsdescribed herein. In either case, for Intra block copy, a predictiveblock may be a block that is deemed as closely matching the block to becoded, in terms of pixel difference, which may be determined by sum ofabsolute difference (SAD), sum of squared difference (SSD), or otherdifference metrics, and identification of the predictive block mayinclude calculation of values for sub-integer pixel positions.

Whether the predictive block is from the same frame according to intraprediction, or a different frame according to inter prediction, videoencoder 20 may form a residual video block by subtracting pixel valuesof the predictive block from the pixel values of the current video blockbeing coded, forming pixel difference values. The pixel differencevalues forming the residual video block may include both luma and chromacomponent differences.

Intra prediction processing unit 46 may intra-predict a current videoblock, as an alternative to the inter-prediction performed by motionestimation unit 42 and motion compensation unit 44, or the intra blockcopy prediction performed by intra BC unit 48, as described above. Inparticular, intra prediction processing unit 46 may determine an intraprediction mode to use to encode a current block. To do so, intraprediction processing unit 46 may encode a current block using variousintra prediction modes, e.g., during separate encoding passes, and intraprediction processing unit 46 (or a mode select unit, in some examples)may select an appropriate intra prediction mode to use from the testedintra prediction modes. Intra prediction processing unit 46 may provideinformation indicative of the selected intra-prediction mode for theblock to entropy encoding unit 56. Entropy encoding unit 56 may encodethe information indicating the selected intra-prediction mode in thebitstream.

After prediction processing unit 41 determines the predictive block forthe current video block via either inter prediction or intra prediction,summer 50 forms a residual video block by subtracting the predictiveblock from the current video block. The residual video data in theresidual block may be included in one or more transform units (TUs) andis provided to transform processing unit 52. Transform processing unit52 transforms the residual video data into residual transformcoefficients using a transform, such as a discrete cosine transform(DCT) or a conceptually similar transform.

Transform processing unit 52 may send the resulting transformcoefficients to quantization unit 54. Quantization unit 54 quantizes thetransform coefficients to further reduce bit rate. The quantizationprocess may also reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, quantization unit 54 may thenperform a scan of a matrix including the quantized transformcoefficients. Alternatively, entropy encoding unit 56 may perform thescan.

Following quantization, entropy encoding unit 56 entropy encodes thequantized transform coefficients into a video bitstream using, e.g.,context adaptive variable length coding (CAVLC), context adaptive binaryarithmetic coding (CABAC), syntax-based context-adaptive binaryarithmetic coding (SBAC), probability interval partitioning entropy(PIPE) coding or another entropy encoding methodology or technique. Theencoded bitstream may then be transmitted to video decoder 30, orarchived in storage device 32 for later transmission to or retrieval byvideo decoder 30. Entropy encoding unit 56 may also entropy encode themotion vectors and the other syntax elements for the current video framebeing coded.

Inverse quantization unit 58 and inverse transform processing unit 60apply inverse quantization and inverse transformation, respectively, toreconstruct the residual video block in the pixel domain for generatinga reference block for prediction of other video blocks. As noted above,motion compensation unit 44 may generate a motion compensated predictiveblock from one or more reference blocks of the frames stored in DPB 64.Motion compensation unit 44 may also apply one or more interpolationfilters to the predictive block to calculate sub-integer pixel valuesfor use in motion estimation.

Summer 62 adds the reconstructed residual block to the motioncompensated predictive block produced by motion compensation unit 44 toproduce a reference block for storage in DPB 64. The reference block maythen be used by intra BC unit 48, motion estimation unit 42 and motioncompensation unit 44 as a predictive block to inter predict anothervideo block in a subsequent video frame.

FIG. 3 is a block diagram illustrating an exemplary video decoder 30 inaccordance with some implementations of the present application. Videodecoder 30 includes video data memory 79, entropy decoding unit 80,prediction processing unit 81, inverse quantization unit 86, inversetransform processing unit 88, summer 90, and DPB 92. Predictionprocessing unit 81 further includes motion compensation unit 82, intraprediction unit 84, and intra BC unit 85. Video decoder 30 may perform adecoding process generally reciprocal to the encoding process describedabove with respect to video encoder 20 in connection with FIG. 2. Forexample, motion compensation unit 82 may generate prediction data basedon motion vectors received from entropy decoding unit 80, whileintra-prediction unit 84 may generate prediction data based onintra-prediction mode indicators received from entropy decoding unit 80.

In some examples, a unit of video decoder 30 may be tasked to performthe implementations of the present application. Also, in some examples,the implementations of the present disclosure may be divided among oneor more of the units of video decoder 30. For example, intra BC unit 85may perform the implementations of the present application, alone, or incombination with other units of video decoder 30, such as motioncompensation unit 82, intra prediction unit 84, and entropy decodingunit 80. In some examples, video decoder 30 may not include intra BCunit 85 and the functionality of intra BC unit 85 may be performed byother components of prediction processing unit 81, such as motioncompensation unit 82.

Video data memory 79 may store video data, such as an encoded videobitstream, to be decoded by the other components of video decoder 30.The video data stored in video data memory 79 may be obtained, forexample, from storage device 32, from a local video source, such as acamera, via wired or wireless network communication of video data, or byaccessing physical data storage media (e.g., a flash drive or harddisk). Video data memory 79 may include a coded picture buffer (CPB)that stores encoded video data from an encoded video bitstream. Decodedpicture buffer (DPB) 92 of video decoder 30 stores reference video datafor use in decoding video data by video decoder 30 (e.g., in intra orinter predictive coding modes). Video data memory 79 and DPB 92 may beformed by any of a variety of memory devices, such as dynamic randomaccess memory (DRAM), including synchronous DRAM (SDRAM),magneto-resistive RAM (MRAM), resistive RAM (RRAM), or other types ofmemory devices. For illustrative purpose, video data memory 79 and DPB92 are depicted as two distinct components of video decoder 30 in FIG.3. But it will be apparent to one skilled in the art that video datamemory 79 and DPB 92 may be provided by the same memory device orseparate memory devices. In some examples, video data memory 79 may beon-chip with other components of video decoder 30, or off-chip relativeto those components.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video frame andassociated syntax elements. Video decoder 30 may receive the syntaxelements at the video frame level and/or the video block level. Entropydecoding unit 80 of video decoder 30 entropy decodes the bitstream togenerate quantized coefficients, motion vectors or intra-prediction modeindicators, and other syntax elements. Entropy decoding unit 80 thenforwards the motion vectors and other syntax elements to predictionprocessing unit 81.

When the video frame is coded as an intra predictive coded (I) frame orfor intra coded predictive blocks in other types of frames,intra-prediction unit 84 of prediction processing unit 81 may generateprediction data for a video block of the current video frame based on asignaled intra prediction mode and reference data from previouslydecoded blocks of the current frame.

When the video frame is coded as an inter-predictive coded (i.e., B orP) frame, motion compensation unit 82 of prediction processing unit 81produces one or more predictive blocks for a video block of the currentvideo frame based on the motion vectors and other syntax elementsreceived from entropy decoding unit 80. Each of the predictive blocksmay be produced from a reference frame within one of the reference framelists. Video decoder 30 may construct the reference frame lists, List 0and List 1, using default construction techniques based on referenceframes stored in DPB 92.

In some examples, when the video block is coded according to the intraBC mode described herein, intra BC unit 85 of prediction processing unit81 produces predictive blocks for the current video block based on blockvectors and other syntax elements received from entropy decoding unit80. The predictive blocks may be within a reconstructed region of thesame picture as the current video block defined by video encoder 20.

Motion compensation unit 82 and/or intra BC unit 85 determinesprediction information for a video block of the current video frame byparsing the motion vectors and other syntax elements, and then uses theprediction information to produce the predictive blocks for the currentvideo block being decoded. For example, motion compensation unit 82 usessome of the received syntax elements to determine a prediction mode(e.g., intra or inter prediction) used to code video blocks of the videoframe, an inter prediction frame type (e.g., B or P), constructioninformation for one or more of the reference frame lists for the frame,motion vectors for each inter predictive encoded video block of theframe, inter prediction status for each inter predictive coded videoblock of the frame, and other information to decode the video blocks inthe current video frame.

Similarly, intra BC unit 85 may use some of the received syntaxelements, e.g., a flag, to determine that the current video block waspredicted using the intra BC mode, construction information of whichvideo blocks of the frame are within the reconstructed region and shouldbe stored in DPB 92, block vectors for each intra BC predicted videoblock of the frame, intra BC prediction status for each intra BCpredicted video block of the frame, and other information to decode thevideo blocks in the current video frame.

Motion compensation unit 82 may also perform interpolation using theinterpolation filters as used by video encoder 20 during encoding of thevideo blocks to calculate interpolated values for sub-integer pixels ofreference blocks. In this case, motion compensation unit 82 maydetermine the interpolation filters used by video encoder 20 from thereceived syntax elements and use the interpolation filters to producepredictive blocks.

Inverse quantization unit 86 inverse quantizes the quantized transformcoefficients provided in the bitstream and entropy decoded by entropydecoding unit 80 using the same quantization parameter calculated byvideo encoder 20 for each video block in the video frame to determine adegree of quantization. Inverse transform processing unit 88 applies aninverse transform, e.g., an inverse DCT, an inverse integer transform,or a conceptually similar inverse transform process, to the transformcoefficients in order to reconstruct the residual blocks in the pixeldomain.

After motion compensation unit 82 or intra BC unit 85 generates thepredictive block for the current video block based on the vectors andother syntax elements, summer 90 reconstructs decoded video block forthe current video block by summing the residual block from inversetransform processing unit 88 and a corresponding predictive blockgenerated by motion compensation unit 82 and intra BC unit 85. Anin-loop filter (not pictured) may be positioned between summer 90 andDPB 92 to further process the decoded video block. The decoded videoblocks in a given frame are then stored in DPB 92, which storesreference frames used for subsequent motion compensation of next videoblocks. DPB 92, or a memory device separate from DPB 92, may also storedecoded video for later presentation on a display device, such asdisplay device 34 of FIG. 1.

In a typical video coding process, a video sequence typically includesan ordered set of frames or pictures. Each frame may include threesample arrays, denoted SL, SCb, and SCr. SL is a two-dimensional arrayof luma samples. SCb is a two-dimensional array of Cb chroma samples.SCr is a two-dimensional array of Cr chroma samples. In other instances,a frame may be monochrome and therefore includes only onetwo-dimensional array of luma samples.

As shown in FIG. 4A, video encoder 20 (or more specifically partitionunit 45) generates an encoded representation of a frame by firstpartitioning the frame into a set of coding tree units (CTUs). A videoframe may include an integer number of CTUs ordered consecutively in araster scan order from left to right and from top to bottom. Each CTU isa largest logical coding unit and the width and height of the CTU aresignaled by the video encoder 20 in a sequence parameter set, such thatall the CTUs in a video sequence have the same size being one of128×128, 64×64, 32×32, and 16×16. But it should be noted that thepresent application is not necessarily limited to a particular size. Asshown in FIG. 4B, each CTU may comprise one coding tree block (CTB) ofluma samples, two corresponding coding tree blocks of chroma samples,and syntax elements used to code the samples of the coding tree blocks.The syntax elements describe properties of different types of units of acoded block of pixels and how the video sequence can be reconstructed atthe video decoder 30, including inter or intra prediction, intraprediction mode, motion vectors, and other parameters. In monochromepictures or pictures having three separate color planes, a CTU maycomprise a single coding tree block and syntax elements used to code thesamples of the coding tree block. A coding tree block may be an N×Nblock of samples.

To achieve a better performance, video encoder 20 may recursivelyperform tree partitioning such as binary-tree partitioning, ternary-treepartitioning, quad-tree partitioning or a combination of both on thecoding tree blocks of the CTU and divide the CTU into smaller codingunits (CUs). As depicted in FIG. 4C, the 64×64 CTU 400 is first dividedinto four smaller CU, each having a block size of 32×32. Among the foursmaller CUs, CU 410 and CU 420 are each divided into four CUs of 16×16by block size. The two 16×16 CUs 430 and 440 are each further dividedinto four CUs of 8×8 by block size. FIG. 4D depicts a quad-tree datastructure illustrating the end result of the partition process of theCTU 400 as depicted in FIG. 4C, each leaf node of the quad-treecorresponding to one CU of a respective size ranging from 32×32 to 8×8.Like the CTU depicted in FIG. 4B, each CU may comprise a coding block(CB) of luma samples and two corresponding coding blocks of chromasamples of a frame of the same size, and syntax elements used to codethe samples of the coding blocks. In monochrome pictures or pictureshaving three separate color planes, a CU may comprise a single codingblock and syntax structures used to code the samples of the codingblock. It should be noted that the quad-tree partitioning depicted inFIGS. 4C and 4D is only for illustrative purposes and one CTU can besplit into CUs to adapt to varying local characteristics based onquad/ternary/binary-tree partitions. In the multi-type tree structure,one CTU is partitioned by a quad-tree structure and each quad-tree leafCU can be further partitioned by a binary and ternary tree structure. Asshown in FIG. 4E, there are five partitioning types, i.e., quaternarypartitioning, horizontal binary partitioning, vertical binarypartitioning, horizontal ternary partitioning, and vertical ternarypartitioning.

In some implementations, video encoder 20 may further partition a codingblock of a CU into one or more M×N prediction blocks (PB). A predictionblock is a rectangular (square or non-square) block of samples on whichthe same prediction, inter or intra, is applied. A prediction unit (PU)of a CU may comprise a prediction block of luma samples, twocorresponding prediction blocks of chroma samples, and syntax elementsused to predict the prediction blocks. In monochrome pictures orpictures having three separate color planes, a PU may comprise a singleprediction block and syntax structures used to predict the predictionblock. Video encoder 20 may generate predictive luma, Cb, and Cr blocksfor luma, Cb, and Cr prediction blocks of each PU of the CU.

Video encoder 20 may use intra prediction or inter prediction togenerate the predictive blocks for a PU. If video encoder 20 uses intraprediction to generate the predictive blocks of a PU, video encoder 20may generate the predictive blocks of the PU based on decoded samples ofthe frame associated with the PU. If video encoder 20 uses interprediction to generate the predictive blocks of a PU, video encoder 20may generate the predictive blocks of the PU based on decoded samples ofone or more frames other than the frame associated with the PU.

After video encoder 20 generates predictive luma, Cb, and Cr blocks forone or more PUs of a CU, video encoder 20 may generate a luma residualblock for the CU by subtracting the CU's predictive luma blocks from itsoriginal luma coding block such that each sample in the CU's lumaresidual block indicates a difference between a luma sample in one ofthe CU's predictive luma blocks and a corresponding sample in the CU'soriginal luma coding block. Similarly, video encoder 20 may generate aCb residual block and a Cr residual block for the CU, respectively, suchthat each sample in the CU's Cb residual block indicates a differencebetween a Cb sample in one of the CU's predictive Cb blocks and acorresponding sample in the CU's original Cb coding block and eachsample in the CU's Cr residual block may indicate a difference between aCr sample in one of the CU's predictive Cr blocks and a correspondingsample in the CU's original Cr coding block.

Furthermore, as illustrated in FIG. 4C, video encoder 20 may usequad-tree partitioning to decompose the luma, Cb, and Cr residual blocksof a CU into one or more luma, Cb, and Cr transform blocks. A transformblock is a rectangular (square or non-square) block of samples on whichthe same transform is applied. A transform unit (TU) of a CU maycomprise a transform block of luma samples, two corresponding transformblocks of chroma samples, and syntax elements used to transform thetransform block samples. Thus, each TU of a CU may be associated with aluma transform block, a Cb transform block, and a Cr transform block. Insome examples, the luma transform block associated with the TU may be asub-block of the CU's luma residual block. The Cb transform block may bea sub-block of the CU's Cb residual block. The Cr transform block may bea sub-block of the CU's Cr residual block. In monochrome pictures orpictures having three separate color planes, a TU may comprise a singletransform block and syntax structures used to transform the samples ofthe transform block.

Video encoder 20 may apply one or more transforms to a luma transformblock of a TU to generate a luma coefficient block for the TU. Acoefficient block may be a two-dimensional array of transformcoefficients. A transform coefficient may be a scalar quantity. Videoencoder 20 may apply one or more transforms to a Cb transform block of aTU to generate a Cb coefficient block for the TU. Video encoder 20 mayapply one or more transforms to a Cr transform block of a TU to generatea Cr coefficient block for the TU.

After generating a coefficient block (e.g., a luma coefficient block, aCb coefficient block or a Cr coefficient block), video encoder 20 mayquantize the coefficient block. Quantization generally refers to aprocess in which transform coefficients are quantized to possibly reducethe amount of data used to represent the transform coefficients,providing further compression. After video encoder 20 quantizes acoefficient block, video encoder 20 may entropy encode syntax elementsindicating the quantized transform coefficients. For example, videoencoder 20 may perform Context-Adaptive Binary Arithmetic Coding (CABAC)on the syntax elements indicating the quantized transform coefficients.Finally, video encoder 20 may output a bitstream that includes asequence of bits that forms a representation of coded frames andassociated data, which is either saved in storage device 32 ortransmitted to destination device 14.

After receiving a bitstream generated by video encoder 20, video decoder30 may parse the bitstream to obtain syntax elements from the bitstream.Video decoder 30 may reconstruct the frames of the video data based atleast in part on the syntax elements obtained from the bitstream. Theprocess of reconstructing the video data is generally reciprocal to theencoding process performed by video encoder 20. For example, videodecoder 30 may perform inverse transforms on the coefficient blocksassociated with TUs of a current CU to reconstruct residual blocksassociated with the TUs of the current CU. Video decoder 30 alsoreconstructs the coding blocks of the current CU by adding the samplesof the predictive blocks for PUs of the current CU to correspondingsamples of the transform blocks of the TUs of the current CU. Afterreconstructing the coding blocks for each CU of a frame, video decoder30 may reconstruct the frame.

As noted above, video coding achieves video compression using primarilytwo modes, i.e., intra-frame prediction (or intra-prediction) andinter-frame prediction (or inter-prediction). Palette-based coding isanother coding scheme that has been adopted by many video codingstandards. In palette-based coding, which may be particularly suitablefor screen-generated content coding, a video coder (e.g., video encoder20 or video decoder 30) forms a palette table of colors representing thevideo data of a given block. The palette table includes the mostdominant (e.g., frequently used) pixel values in the given block. Pixelvalues that are not frequently represented in the video data of thegiven block are either not included in the palette table or included inthe palette table as escape colors.

Each entry in the palette table includes an index for a correspondingpixel value that in the palette table. The palette indices for samplesin the block may be coded to indicate which entry from the palette tableis to be used to predict or reconstruct which sample. This palette modestarts with the process of generating a palette predictor for a firstblock of a picture, slice, tile, or other such grouping of video blocks.As will be explained below, the palette predictor for subsequent videoblocks is typically generated by updating a previously used palettepredictor. For illustrative purpose, it is assumed that the palettepredictor is defined at a picture level. In other words, a picture mayinclude multiple coding blocks, each having its own palette table, butthere is one palette predictor for the entire picture.

To reduce the bits needed for signaling palette entries in the videobitstream, a video decoder may utilize a palette predictor fordetermining new palette entries in the palette table used forreconstructing a video block. For example, the palette predictor mayinclude palette entries from a previously used palette table or even beinitialized with a most recently used palette table by including allentries of the most recently used palette table. In someimplementations, the palette predictor may include fewer than all theentries from the most recently used palette table and then incorporatesome entries from other previously used palette tables. The palettepredictor may have the same size as the palette tables used for codingdifferent blocks or may be larger or smaller than the palette tablesused for coding different blocks. In one example, the palette predictoris implemented as a first-in-first-out (FIFO) table including 64 paletteentries.

To generate a palette table for a block of video data from the palettepredictor, a video decoder may receive, from the encoded videobitstream, a one-bit flag for each entry of the palette predictor. Theone-bit flag may have a first value (e.g., a binary one) indicating thatthe associated entry of the palette predictor is to be included in thepalette table or a second value (e.g., a binary zero) indicating thatthe associated entry of the palette predictor is not to be included inthe palette table. If the size of palette predictor is larger than thepalette table used for a block of video data, then the video decoder maystop receiving more flags once a maximum size for the palette table isreached.

In some implementations, some entries in a palette table may be directlysignaled in the encoded video bitstream instead of being determinedusing the palette predictor. For such entries, the video decoder mayreceive, from the encoded video bitstream, three separate m-bit valuesindicating the pixel values for the luma and two chroma componentsassociated with the entry, where m represents the bit depth of the videodata. Compared with the multiple m-bit values needed for directlysignaled palette entries, those palette entries derived from the palettepredictor only require a one-bit flag. Therefore, signaling some or allpalette entries using the palette predictor can significantly reduce thenumber of bits needed to signal the entries of a new palette table,thereby improving the overall coding efficiency of palette mode coding.

In many instances, the palette predictor for one block is determinedbased on the palette table used to code one or more previously codedblocks. But when coding the first coding tree unit in a picture, a sliceor a tile, the palette table of a previously coded block may not beavailable. Therefore a palette predictor cannot be generated usingentries of the previously used palette tables. In such case, a sequenceof palette predictor initializers may be signaled in a sequenceparameter set (SPS) and/or a picture parameter set (PPS), which arevalues used to generate a palette predictor when a previously usedpalette table is not available. An SPS generally refers to a syntaxstructure of syntax elements that apply to a series of consecutive codedvideo pictures called a coded video sequence (CVS) as determined by thecontent of a syntax element found in the PPS referred to by a syntaxelement found in each slice segment header. A PPS generally refers to asyntax structure of syntax elements that apply to one or more individualpictures within a CVS as determined by a syntax element found in eachslice segment header. Thus, an SPS is generally considered to be ahigher level syntax structure than a PPS, meaning the syntax elementsincluded in the SPS generally change less frequently and apply to alarger portion of video data compared to the syntax elements included inthe PPS.

FIG. 5 is a block diagram illustrating different prediction modes of acoding unit in accordance with some implementations of the presentdisclosure.

In VVC, each CU can be coded as skip mode or non-skip mode. For a CUcoded as skip mode, one syntax element is further signaled to indicatewhether the current CU is regular skip mode (similar to the skip mode inHEVC) or IBC skip mode. For a CU coded as non-skip mode, syntax elementsare further signaled to indicate if the current CU is coded as intramode, inter mode, intra block copy (IBC) mode or palette (PLT) mode.These modes are termed as “MODE_INTRA”, “MODE_INTER”, “MODE_IBC” and“MODE_PLT” respectively in the VVC specification. For a CU coded asintra mode, only the spatial neighboring reconstructed pixels in thesame picture/slice could be used to generate the prediction signal forthe current CU. For a CU coded as inter mode, the prediction signal canbe generated by pixels from the reference pictures which are not thecurrent picture. The detail of IBC mode could be found in documentJVET-N1002 (at http://phenix.int-evry.fr/jvet/). The palette (PLT) modeis newly adopted into VVC in 15^(th) JVET meeting with details explainedin the document JVET-00119 located at http://phenix.int-evry.fr/jvet/.

In the current VVC, the constraints and conditions for enabling eachdifferent mode are different, as summarized in Table 1 below. Moreover,a flag is signaled in sequence parameter set (SPS) to indicate theon/off of the IBC and PLT modes, i.e. indicating whether IBC and/or PLTmode are allowed in the associated bitstream.

TABLE 1 Constrains of enabling/signaling the non-skip related modesConstraints of mode enabling/signaling intra mode no constraints intermode (block width × block height)>16 IBC mode block width <=64 && blockheight <=64 && sps_ibc_enabled_flag && treeType  !=  DUAL_TREE_CHROMAPLT mode block width <=64 && block height <=64 && sps_plt_enabled_flag

The syntax of the mode signaling in current VVC is illustrated in thetable below.

TABLE 2 Syntax of prediction modes signaling in current VVC coding_unit(x0, y0, cbWidth, cbHeight, cqtDepth, treeType, modeType ) { Descriptor chType = treeType = = DUAL_TREE_CHROMA? 1 : 0  if( slice_type != I | |sps_ibc_enabled_flag | | sps_palette_enabled_flag) {   if( treeType !=DUAL_TREE_CHROMA &&    !( ( ( cbWidth = = 4 && cbHeight = = 4 ) | |modeType = = MODE_TYPE_INTRA )      && !sps_ibc_enabled flag ) )    cu_skip_flag[ x0 ][ y0 ] ae(v)   if( cu_skip_flag[ x0 ][ y0 ] = = 0&& slice_type != I    && !( cbWidth = = 4 && cbHeight = = 4 ) &&modeType = = MODE_TYPE_ALL )     pred_mode_flag ae(v)   if( ( ( slicetype = = I && cu_skip_flag[ x0 ][ y0 ] = = 0 ) | |       ( slice_type !=I && ( CuPredMode[ chType ][ x0 ][ y0 ] != MODE_INTRA | |         (cbWidth = = 4 && cbHeight = = 4 && cu_skip_flag[ x0 ][ y0 ] = = 0 ) ) )) &&      cbWidth <= 64 && cbHeight <= 64 && modeType != MODE_TYPE_INTER&&      sps_ibc_enabled_flag && treeType != DUAL_TREE_CHROMA )    pred_mode_ibc_flag ae(v)   if( ( ( ( slice_type = = I | | ( cbWidth= = 4 && cbHeight = = 4 ) | | sps_ibc_enabled_flag ) &&        CuPredMode[ x0 ][ y0 ] = = MODE_INTRA ) | |       ( slice_type!= I && !( cbWidth = = 4 && cbHeight = = 4 ) && !sps_ibc_enabled_flag       && CuPredMode[ x0 ][ y0 ] != MODE_INTRA ) ) &&sps_palette_enabled_flag &&       cbWidth <= 64 && cbHeight <= 64 && &&cu_skip_flag[ x0 ][ y0 ] = = 0 &&       modeType != MODE_INTER )    pred_mode_plt_flag ae(v)  }

The semantic of the mode signaling in current VVC is illustrated below.

cu_skip_flag[x0][y0] equal to 1 specifies that for the current codingunit, when decoding a P or B slice, no more syntax elements except oneor more of the following are parsed after cu_skip_flag[x0][y0]: the IBCmode flag pred_mode_ibc_flag [x0][y0], and the merge_data( ) syntaxstructure; when decoding an I slice, no more syntax elements exceptmerge_idx[x0][y0] are parsed after cu_skip_flag[x0][y0].cu_skip_flag[x0][y0] equal to 0 specifies that the coding unit is notskipped. The array indices x0, y0 specify the location (x0, y0) of thetop-left luma sample of the considered coding block relative to thetop-left luma sample of the picture. When cu_skip_flag[x0][y0] is notpresent, it is inferred to be equal to 0.

pred_mode_flag equal to 0 specifies that the current coding unit iscoded in inter prediction mode. pred_mode_flag equal to 1 specifies thatthe current coding unit is coded in intra prediction mode. Whenpred_mode_flag is not present, it is inferred as follows:

-   -   If cbWidth is equal to 4 and cbHeight is equal to 4,        pred_mode_flag is inferred to be equal to 1.    -   Otherwise, if modeType is equal to MODE_TYPE_INTRA,        pred_mode_flag is inferred to be equal to 1.    -   Otherwise, if modeType is equal to MODE_TYPE_INTER,        pred_mode_flag is inferred to be equal to 0.    -   Otherwise, pred_mode_flag is inferred to be equal to 1 when        decoding an I slice, and equal to 0 when decoding a P or B        slice, respectively.    -   The variable CuPredMode[chType][x][y] is derived as follows for        x=x0 . . . x0+cbWidth−1 and y=y0 . . . y0+cbHeight−1:    -   If pred_mode_flag is equal to 0, CuPredMode[chType][x][y] is set        equal to MODE_INTER.    -   Otherwise (pred_mode_flag is equal to 1),        CuPredMode[chType][x][y] is set equal to MODE_INTRA.

pred_mode_ibc_flag equal to 1 specifies that the current coding unit iscoded in IBC prediction mode. pred_mode_ibc_flag equal to 0 specifiesthat the current coding unit is not coded in IBC prediction mode. Whenpred_mode_ibc_flag is not present, it is inferred as follows:

-   -   If cu_skip_flag[x0][y0] is equal to 1, and cbWidth is equal to        4, and cbHeight is equal to 4, pred_mode_ibc_flag is inferred to        be equal 1.    -   Otherwise, if both cbWidth and cbHeight are equal to 128,        pred_mode_ibc_flag is inferred to be equal to 0.    -   Otherwise, if modeType is equal to MODE_TYPE_INTER,        pred_mode_ibc_flag is inferred to be equal to 0.    -   Otherwise, if treeType is equal to DUAL TREE CHROMA,        pred_mode_ibc_flag is inferred to be equal to 0.    -   Otherwise, pred_mode_ibc_flag is infered to be equal to the        value of sps_ibc_enabled_flag when decoding an I slice, and 0        when decoding a P or B slice, respectively.    -   When pred_mode_ibc_flag is equal to 1, the variable        CuPredMode[chType][x][y] is set to be equal to MODE_IBC for x=x0        . . . x0+cbWidth−1 and y=y0 . . . y0+cbHeight−1.

pred_mode_plt_flag specifies the use of palette mode in the currentcoding unit. pred_mode_plt_flag equal to 1 indicates that palette modeis applied in the current coding unit. pred_mode_plt_flag equal to 0indicates that palette mode is not applied in the current coding unit.When pred_mode_plt_flag is not present, it is inferred to be equal to 0.When pred_mode_plt_flag is equal to 1, the variable CuPredMode[x][y] isset to be equal to MODE_PLT for x=x0 . . . x0+cbWidth−1 and y=y0 . . .y0+cbHeight−1.

To summarize, in current VVC, the syntax (i.e. the associated flags)signaled to indicate the corresponding non-skip modes is shown in Table4 to Table 10, with each table corresponding to different conditions ofprediction modes allowed. It should be noted that in these tables the 0and 1 in the codewords may all be inverted and the resulted codewordswould function equally. Moreover, the naming of the syntax elements canalso be changed to other names without changing the function of thesignaled modes.

TABLE 3 Signaling of the non-skip CU prediction modes in current VVCwhen all the modes (inter, inter, IBC and PLT modes) are allowedPred_Modes pred_mode_flag pred_mode_ibc_flag pred_mode_plt_flag INTER 00 — IBC 0 1 — PLT 1 — 1 INTRA 1 — 0

TABLE 4 Signaling of the non-skip CU modes in current VVC when onlyintra, IBC and PLT modes are allowed Pred_Modes pred_mode_flagpred_mode_ibc_flag pred_mode_plt_flag IBC — 1 — PLT — 0 1 INTRA — 0 0

TABLE 5 Signaling of the non-skip CU modes in current VVC when onlyintra, inter and PLT modes are allowed Pred_Modes pred_mode_flagpred_mode_ibc_flag pred_mode_plt_flag INTER 0 — 0 PLT 0 — 1 INTRA 1 — —

TABLE 6 Signaling of the non-skip CU modes in current VVC when onlyintra, inter and IBC modes are allowed Pred_Modes pred_mode_flagpred_mode_ibc_flag pred_mode_plt_flag INTER 0 0 — IBC 0 1 — INTRA 1 — —

TABLE 7 Signaling of the non-skip CU modes in current VVC when onlyintra and IBC modes are allowed Pred_Modes pred_mode_flagpred_mode_ibc_flag pred_mode_plt_flag IBC — 1 — INTRA — 0 —

TABLE 8 Signaling of the non-skip CU modes in current VVC when onlyintra and PLT modes are allowed Pred_Modes pred_mode_flagpred_mode_ibc_flag pred_mode_plt_flag PLT — — 1 INTRA — — 0

TABLE 9 Signaling of the non-skip CU modes in current VVC when onlyintra and inter modes are allowed Pred_Modes pred_mode_flagpred_mode_ibc_flag pred_mode_plt_flag INTER 0 — — INTRA 1 — —

FIG. 6 is a flowchart illustrating an exemplary process by which a videocoder implements the techniques of signaling prediction mode inaccordance with some implementations of the present disclosure.

In current VVC, the IBC mode is regarded as a mode which is more similarto the inter mode while the PLT mode is regarded as a mode more similarto the intra mode. Therefore, in VVC, the IBC mode flag(pred_mode_ibc_flag) is signaled when the pred_mode_flag is signaled as0 which implies the current CU is inter mode alike. The PLT mode flag(pred_mode_plt_flag) is signaled when the pred_mode_flag is signaled as1 which implies the current CU is intra mode alike. However, there isone exception when only intra, inter and PLT modes are allowed (i.e. IBCmode is not allowed). As shown in Table 5, The PLT mode flag(pred_mode_plt_flag) is signaled when the pred_mode_flag is signaled as0. Such an exception not only breaks the physical meaning of the flag ofpred_mode_flag, it also complicates the signaling conditions ofpred_mode_plt_flag because different signaling conditions are useddepending on whether IBC mode is allowed or not.

Moreover, in current VVC, the condition checking to signal thepred_mode_ibc_flag and pred_mode_plt_flag is complex as shown in Table2. Several methods are proposed to simplify the condition checking insignaling these prediction modes.

According to the first embodiment of the disclosure, the flag toindicate the enabling of the palette mode (e.g. pred_mode_plt_flag inVVC specification) is signaled only under intra-like mode, regardless ofthe conditions of prediction modes allowed. In one example, only whenthe syntax element used to indicate the intra-like or inter-like mode(e.g. pred_mode_flag) is signaled or inferred as intra-like mode (e.g.signaling pred_mode_flag as 1 in current VVC), the palette mode flagpred_mode_plt_flag is signaled. According to the embodiment, when onlyinter, intra and PLT modes are allowed, the corresponding codewords areillustrated in Table 10. It is different from Table 5. Moreover, thesignaling conditions of pred_mode_plt_flag can be simplified ashighlighted in Table 11.

TABLE 10 Signaling of the non-skip CU modes when only intra, inter andPLT modes are allowed based on the first embodiment Pred_Modespred_mode_flag pred_mode_ibc_flag pred_mode_plt_flag INTER 0 — — PLT 1 —1 INTRA 1 — 0

TABLE 11 Syntax of proposed mode signaling for VVC (the modified partsare highlighted) coding_unit( x0, y0, cbWidth, cbHeight, cqtDepth,treeType, modeType ) { Descriptor  chType = treeType = =DUAL_TREE_CHROMA? 1 : 0  if( slice_type != I | | sps_ibc_enabled_flag || sps_palette_enabled_flag) {   if( treeType != DUAL_TREE_CHROMA &&   !( ( ( cbWidth = = 4 && cbHeight = = 4 ) | | modeType = =MODE_TYPE_INTRA )      && !sps_ibc_enabled_flag ) )     cu_skip_flag[ x0][ y0 ] ae(v)   if( cu_skip_flag[ x0 ][ y0 ] = = 0 && slice_type != I   && !( cbWidth = = 4 && cbHeight = = 4 ) && modeType = = MODE_TYPE_ALL)     pred_mode_flag ae(v)   if( ( ( slice_type = = I && cu_skip_flag[x0 ][ y0 ] = = 0 ) | |       ( slice_type != I && ( CuPredMode[ chType][ x0 ][ y0 ] != MODE_INTRA | |        ( cbWidth = = 4 && cbHeight = = 4&& cu_skip_flag[ x0 ][ y0 ] = = 0 ) ) ) ) &&      cbWidth <= 64 &&cbHeight <= 64 && modeType != MODE_TYPE_INTER &&     sps_ibc_enabled_flag && treeType != DUAL_TREE_CHROMA )    pred_mode_ibc_flag ae(v)  if( ( CuPredMode[ x0 ][ y0 ] = =MODE_INTRA ) && sps_palette_enabled_flag &&       cbWidth <= 64 &&cbHeight <= 64 && && cu_skip_flag[ x0 ][ y0 ] = = 0 &&       modeType !=MODE_INTER )     pred_mode_plt_flag ae(v)  } (...the rest of the specfor the coding unit) }

According to the second embodiment of the disclosure, the modes aresignaled based on a predefined order, with each mode indicated through acorresponding flag except the very last mode. The very last mode doesnot need a corresponding flag because it can be inferred as enabled whenall the previously signaled modes (or flags) are not enabled. In oneexample, inter mode, IBC mode and PLT mode are respectively indicatedthrough a flag pred_mode_inter_flag, pred_mode_ibc_flag andpred_mode_plt_flag. In this case, the method is basically identical toassigning the truncated binary codewords to the modes based on apredefined order of signaling. The associated codewords are illustratedin Table 12 to Table 18. The signaling conditions of pred_mode_ibc_flagand pred_mode_plt_flag can also be simplified, as highlighted in Table19.

TABLE 12 Signaling of the non-skip CU modes when all the modes (inter,inter, IBC and PLT modes) are allowed, based on the second embodimentPred_ pred_mode_ pred_mode_ pred_mode_ Modes inter_flag ibc_flagplt_flag INTER 1 — — IBC 0 1 — PLT 0 0 1 INTRA 0 0 0

TABLE 13 Signaling of the non-skip CU modes when only intra, IBC and PLTmodes are allowed, based on the second embodiment Pred_ pred_mode_pred_mode_ pred_mode_ Modes inter_flag ibc_flag plt_flag IBC — 1 — PLT —0 1 INTRA — 0 0

TABLE 14 Signaling of the non-skip CU modes when only intra, inter andPLT modes are allowed, based on the second embodiment Pred_ pred_mode_pred_mode_ pred_mode_ Modes inter_flag ibc_flag plt_flag INTER 1 — — PLT0 — 1 INTRA 0 — 0

TABLE 15 Signaling of the non-skip CU modes when only intra, inter andIBC modes are allowed, based on the second embodiment Pred_ pred_mode_pred_mode_ pred_mode_ Modes inter_flag ibc_flag plt_flag INTER 1 — — IBC0 1 — INTRA 0 0 —

TABLE 16 Signaling of the non-skip CU modes when only intra and IBCmodes are allowed, based on the second embodiment Pred_ pred_mode_pred_mode_ pred_mode_ Modes inter_flag ibc_flag plt_flag IBC — 1 — INTRA— 0 —

TABLE 17 Signaling of the non-skip CU modes when only intra and PLTmodes are allowed, based on the second embodiment Pred_ pred_mode_pred_mode_ pred_mode_ Modes inter_flag ibc_flag plt_flag PLT — — 1 INTRA— — 0

TABLE 18 Signaling of the non-skip CU modes when only intra and intermodes are allowed, based on the second embodiment Pred_ pred_mode_pred_mode_ pred_mode_ Modes inter_flag ibc_flag plt_flag INTER 1 — —INTRA 0 — —

TABLE 19 Syntax of proposed mode signaling for VVC (the modified partsare highlighted) coding_unit( x0, y0, cbWidth, cbHeight, cqtDepth,treeType, modeType ) { Descriptor  chType = treeType = =DUAL_TREE_CHROMA? 1 : 0  if( slice_type != I | | sps_ibc_enabled_flag || sps_palette_enabled_flag) {   if( treeType != DUAL_TREE_CHROMA &&   !( ( ( cbWidth = = 4 && cbHeight = = 4 )| | modeType = =MODE_TYPE_INTRA )      && !sps_ibc_enabled_flag ) )     cu_skip_flag[ x0][ y0 ] ae(v)   if( cu_skip_flag[ x0 ][ y0 ] = = 0 && slice_type != I   && !( cbWidth = = 4 && cbHeight = = 4 ) && modeType = = MODE_TYPE_ALL)     pred_mode_inter_flag ae(v)   if( ( ( slice_type = = I &&cu_skip_flag[ x0 ][ y0 ] = = 0 ) | |       ( slice_type != I &&CuPredMode[ x0 ][ y0 ] = = MODE_INTRA ) ) &&      cbWidth <= 64 &&cbHeight <= 64 && modeType != MODE_TYPE_INTER &&     sps_ibc_enabled_flag && treeType != DUAL_TREE_CHROMA )    pred_mode_ibc_flag ae(v)   if( ( CuPredMode[ x0 ][ y0 ] = =MODE_INTRA ) && sps_palette_enabled_flag &&      cbWidth <= 64 &&cbHeight <= 64 && && cu_skip_flag[ x0 ][ y0 ] = = 0 &&      modeType !=MODE_INTER )     pred_mode_plt_flag ae(v)  }

According to the third embodiment of the disclosure, the modes aresignaled by first sending a syntax element to indicate whether theregular modes (such as inter and intra modes) or the new modes (such asthe IBC and PLT modes) are used by the current block. After the firstsyntax element, additional syntax elements are signaled to indicatewhich mode is used. The associated codewords are illustrated in Table 20to Table 26. It is noted that naming of the codeword bins (or flags) ischanged to reflect their physical meaning according to this embodiment.

TABLE 20 Signaling of the non-skip CU modes when all the modes (inter,inter, IBC and PLT modes) are allowed, based on the third embodimentpred_mode_ pred_mode_ pred_mode_ Pred_Modes regular_flag inter_flagibc_flag INTER 1 1 — IBC 0 — 1 PLT 0 — 0 INTRA 1 0 —

TABLE 21 Signaling of the non-skip CU modes when only intra, IBC and PLTmodes are allowed, based on the third embodiment pred_mode_ pred_mode_pred_mode_ Pred_Modes regular_flag inter_flag ibc_flag IBC 0 — 1 PLT 0 —0 INTRA 1 — —

TABLE 22 Signaling of the non-skip CU modes when only intra, inter andPLT modes are allowed, based on the third embodiment pred_mode_pred_mode_ pred_mode_ Pred_Modes regular_flag inter_flag ibc_flag INTER1 1 — PLT 0 — — INTRA 1 0 —

TABLE 23 Signaling of the non-skip CU modes when only intra, inter andIBC modes are allowed, based on the third embodiment pred_mode_pred_mode_ pred_mode_ Pred_Modes regular_flag inter_flag ibc_flag INTER1 1 — IBC 0 — — INTRA 1 0 —

TABLE 24 Signaling of the non-skip CU modes when only intra and IBCmodes are allowed, based on the third embodiment pred_mode_ pred_mode_pred_mode_ Pred_Modes regular_flag inter_flag ibc_flag IBC 0 — — INTRA 1— —

TABLE 25 Signaling of the non-skip CU modes when only intra and PLTmodes are allowed, based on the third embodiment pred_mode_ pred_mode_pred_mode_ Pred_Modes regular_flag inter_flag ibc_flag PLT 0 — — INTRA 1— —

TABLE 26 Signaling of the non-skip CU modes when only intra and intermodes are allowed, based on the third embodiment pred_mode_ pred_mode_pred_mode_ Pred_Modes regular_flag inter_flag ibc_flag INTER — 1 — INTRA— 0 —

To signal a prediction mode, the video coder first receives, frombitstream, video data corresponding to a non-skip mode coded block (610)and determines a parameter set associated with the non-skip mode codedblock (620). The parameter set (e.g., a sequence parameter set) includesinformation to include which mode (e.g., IBC, PLT, etc) is allowed inthe associated bitstream, as indicated by Table 1.

Next, the video coder selectively receives a first, second, or thirdsyntax elements from the bitstream. If the parameter set includesinformation that satisfies a first condition, the video coder retrievesa first syntax element (e.g., pre_mode_flag in Table 2) from thebitstream (630). If the parameter set includes information thatsatisfies a second condition, the video coder retrieves a second syntaxelement (e.g., pre_mode_ibc_flag in Table 2) from the bitstream (640).If the parameter set includes information that satisfies a thirdcondition, the video coder retrieves a third syntax element (e.g.,pre_mode_plt_flag in Table 2) from the bitstream (650). For theconditions associated with each of the respective syntax elements, referto Table 2. In some embodiments, if a respective condition is notsatisfied, the video coder does not receive the respective syntaxelement (e.g., the video coder may assign default values to the syntaxelements or do not use the syntax elements during decoding).

Next, the video coder decodes the video data corresponding to thenon-skip mode coded block using a respective mode, depending on thevalues of the received first, second, and third syntax elements. Inparticular:

The video coder decodes the video data using palette mode when both thefirst syntax element (e.g, pred_mode_flag in Table 1) and the thirdsyntax element (e.g., pre_mode_plt_flag in Table 1) have a first value(e.g., “1”), and the second condition is not satisfied (e.g., the videocoder does not receive pre_mode_ibc_flag) (660).

The video coder decodes the video data using intra prediction mode whenthe first syntax element (e.g., pred_mode_flag in Table 1) has the firstvalue (e.g., “1”) and the third syntax element has a second value (e.g.,“0”). The second condition is not satisfied (e.g., the video coder doesnot receive pred_mode_ibc_flag) (670).

The video coder decodes the video data using inter prediction mode whenthe first syntax element has the second value (e.g., “0”) and the secondand the third conditions are not satisfied (e.g., the video coder doesnot receive pred_mode_ibc_flag and pre_mode_plt_flag) (680).

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over, as oneor more instructions or code, a computer-readable medium and executed bya hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the implementationsdescribed in the present application. A computer program product mayinclude a computer-readable medium.

The terminology used in the description of the implementations herein isfor the purpose of describing particular implementations only and is notintended to limit the scope of claims. As used in the description of theimplementations and the appended claims, the singular forms “a,” “an,”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will also be understood that theterm “and/or” as used herein refers to and encompasses any and allpossible combinations of one or more of the associated listed items. Itwill be further understood that the terms “comprises” and/or“comprising,” when used in this specification, specify the presence ofstated features, elements, and/or components, but do not preclude thepresence or addition of one or more other features, elements,components, and/or groups thereof.

It will also be understood that, although the terms first, second, etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first electrode could be termeda second electrode, and, similarly, a second electrode could be termed afirst electrode, without departing from the scope of theimplementations. The first electrode and the second electrode are bothelectrodes, but they are not the same electrode.

The description of the present application has been presented forpurposes of illustration and description, and is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications, variations, and alternative implementations will beapparent to those of ordinary skill in the art having the benefit of theteachings presented in the foregoing descriptions and the associateddrawings. The embodiment was chosen and described in order to bestexplain the principles of the invention, the practical application, andto enable others skilled in the art to understand the invention forvarious implementations and to best utilize the underlying principlesand various implementations with various modifications as are suited tothe particular use contemplated. Therefore, it is to be understood thatthe scope of claims is not to be limited to the specific examples of theimplementations disclosed and that modifications and otherimplementations are intended to be included within the scope of theappended claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: receiving, from bitstream, video data corresponding to anon-skip mode coded block; determining a parameter set associated withthe non-skip mode coded block; in accordance with a determination thatthe parameter set includes information that satisfies a first condition,retrieving a first syntax element from the bitstream; in accordance witha determination that the parameter set includes information thatsatisfies a second condition, retrieving a second syntax element fromthe bitstream; in accordance with a determination that the parameter setincludes information that satisfies a third condition, retrieving athird syntax element from the bitstream; decoding the video datacorresponding to the non-skip mode coded block using palette mode whenthe first syntax element has a first value and the third syntax elementhas the first value; decoding the video data corresponding to thenon-skip mode coded block using intra prediction mode when the firstsyntax element has the first value and the third syntax element has asecond value; and decoding the video data corresponding to the non-skipmode coded block using inter prediction mode when the first syntaxelement has the second value.
 2. The method of claim 1, wherein when thevideo data corresponding to the non-skip mode coded block is decodedusing the palette mode, the second condition is not satisfied and thesecond syntax element is not received.
 3. The method of claim 1, whereinwhen the video data corresponding to the non-skip mode coded block isdecoded using the intra prediction mode, the second condition is notsatisfied and the second syntax element is not received.
 4. The methodof claim 1, wherein when the video data corresponding to the non-skipmode coded block is decoded using the inter prediction mode, the secondand the third conditions are not satisfied and the second and the thirdsyntax elements are not received.
 5. The method of claim 1, furthercomprising: decoding the video data corresponding to the non-skip modecoded block using intra block copy mode when the first syntax elementhas a second value or the first syntax element is not received, thesecond syntax element has the first value, and the third syntax elementis not received.
 6. A computing device comprising: one or moreprocessors; memory coupled to the one or more processors; and aplurality of programs stored in the memory that, when executed by theone or more processors, cause the computing device to perform operationscomprising: receiving, from bitstream, video data corresponding to anon-skip mode coded block; determining a parameter set associated withthe non-skip mode coded block; in accordance with a determination thatthe parameter set includes information that satisfies a first condition,retrieving a first syntax element from the bitstream; in accordance witha determination that the parameter set includes information thatsatisfies a second condition, retrieving a second syntax element fromthe bitstream; in accordance with a determination that the parameter setincludes information that satisfies a third condition, retrieving athird syntax element from the bitstream; decoding the video datacorresponding to the non-skip mode coded block using palette mode whenthe first syntax element has a first value and the third syntax elementhas the first value; decoding the video data corresponding to thenon-skip mode coded block using intra prediction mode when the firstsyntax element has the first value and the third syntax element has asecond value; and decoding the video data corresponding to the non-skipmode coded block using inter prediction mode when the first syntaxelement has the second value.
 7. The device of claim 6, wherein when thevideo data corresponding to the non-skip mode coded block is decodedusing the palette mode, the second condition is not satisfied and thesecond syntax element is not received.
 8. The device of claim 6, whereinwhen the video data corresponding to the non-skip mode coded block isdecoded using the intra prediction mode, the second condition is notsatisfied and the second syntax element is not received.
 9. The deviceof claim 6, wherein when the video data corresponding to the non-skipmode coded block is decoded using the inter prediction mode, the secondand the third conditions are not satisfied and the second and the thirdsyntax elements are not received.
 10. The device of claim 6, theoperations further comprising: decoding the video data corresponding tothe non-skip mode coded block using intra block copy mode when the firstsyntax element has a second value or the first syntax element is notreceived, the second syntax element has the first value, and the thirdsyntax element is not received.
 11. A non-transitory computer-readablestorage medium storing computer-readable instructions that, whenexecuted by a decoding apparatus, cause the decoding apparatus toperform operations comprising: receiving, from bitstream, video datacorresponding to a non-skip mode coded block; determining a parameterset associated with the non-skip mode coded block; in accordance with adetermination that the parameter set includes information that satisfiesa first condition, retrieving a first syntax element from the bitstream;in accordance with a determination that the parameter set includesinformation that satisfies a second condition, retrieving a secondsyntax element from the bitstream; in accordance with a determinationthat the parameter set includes information that satisfies a thirdcondition, retrieving a third syntax element from the bitstream;decoding the video data corresponding to the non-skip mode coded blockusing palette mode when the first syntax element has a first value andthe third syntax element has the first value; decoding the video datacorresponding to the non-skip mode coded block using intra predictionmode when the first syntax element has the first value and the thirdsyntax element has a second value; and decoding the video datacorresponding to the non-skip mode coded block using inter predictionmode when the first syntax element has the second value.
 12. Thenon-transitory computer-readable storage medium of claim 11, whereinwhen the video data corresponding to the non-skip mode coded block isdecoded using the palette mode, the second condition is not satisfiedand the second syntax element is not received.
 13. The non-transitorycomputer-readable storage medium of claim 11, wherein when the videodata corresponding to the non-skip mode coded block is decoded using theintra prediction mode, the second condition is not satisfied and thesecond syntax element is not received.
 14. The non-transitorycomputer-readable storage medium of claim 11, wherein when the videodata corresponding to the non-skip mode coded block is decoded using theinter prediction mode, the second and the third conditions are notsatisfied and the second and the third syntax elements are not received.15. The non-transitory computer-readable storage medium of claim 11,wherein the operations further comprise: decoding the video datacorresponding to the non-skip mode coded block using intra block copymode when the first syntax element has a second value or the firstsyntax element is not received, the second syntax element has the firstvalue, and the third syntax element is not received.